NWS Forecast Discussion

000
FXUS63 KMPX 141923
AFDMPX
Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
223 PM CDT Tue Aug 14 2018
.SHORT TERM...(This evening through Wednesday)
Issued at 218 PM CDT Tue Aug 14 2018
The main forecast concern is initiation of thunderstorms along two
boundaries depicted on regional radar and satellite imagery this
afternoon. The first was located just south of the Twin Cities,
with a diffuse area in south central Minnesota where earlier
convection had dissipated prior to 2 pm. The second area was near
Willmar, east-northeast to Elk River and northeast into northwest
Wisconsin. Between these two areas, a dense cirrus shield had led
to lower temperatures and limiting the potential of convective
initiation. However, with the mid-level short wave still west of
west central/central Minnesota and ample mid-level moisture
remaining across southern Minnesota into west central Wisconsin,
the potential is high that thunderstorms will continue to increase
in areal coverage between these two boundaries this afternoon.
Once the sun sets, coverage will decrease along with the activity
slowly propagating to the southeast across southern Minnesota. I
wouldn`t be surprised to see additional activity develop toward
sunrise if a weak low level jet develops along the weak front
sagging into far southern Minnesota. Most of the thunderstorms
should be across Iowa and into southern Wisconsin by Wednesday
afternoon as the main short wave holds south of the area. Only far
southwest/south central Minnesota may see a few showers or storms
Wednesday afternoon if the current upper level low in Montana
meanders further to the north across South Dakota, and northwest
Iowa Wednesday afternoon.
.LONG TERM...(Wednesday night through Tuesday)
Issued at 218 PM CDT Tue Aug 14 2018
Overall, there is very little change from the previous forecast
into this one as the models have remained fairly consistent in the
idea of a split flow pattern keeping the area mostly dry through
the rest of this week with a little more active pattern for next
week.
Wednesday night through Saturday...A upper level ridge over the
western CONUS midweek will ever-so-slowly nudge itself east over
the Rockies and extend into the Northern Plains during the latter
portion of the week. The incoming ridge will help suppress to the
south a weak mid-to-upper level shortwave which may produce a few
isolated showers over far southern portions of the WFO MPX
coverage area Wednesday night into Thursday. Otherwise, the area
will remain dry with building heights aloft and general surface
high pressure prevailing over the area. The main result will be a
slight uptick in temperatures from the midweek period into the
weekend. Highs will climb from around 80 degrees on Thursday to
the mid-80s on Friday and Saturday.
Sunday through Tuesday...Several factors will come into play
during the start of next week which will force the inclusion of
chance-range pops for early next week. A potent upper level
shortwave will drive southeast from western Canada, evolving into
a deep upper level low over the Hudson Bay area with weaker
shortwaves riding around the periphery of the upper low. At the
surface, a cold front will drop into the region from south-central
Canada then stall out over MN/WI Sunday-Tuesday. In addition, a
plume of western GOMEX moisture will be shunted well north into
the Mid-and-Upper Mississippi River Valley regions around the
Bermuda High, giving the features at the surface and aloft
moisture to work with to produce at least scattered showers and
storms early next week. These features will also act to bump down
temperatures once again for the early portion of next week. Highs
will drop into the mid-to-upper 70s with lows back into the 50s.
&&
.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1215 PM CDT Tue Aug 14 2018
Ample, deep moisture, an upper short wave, and a frontal boundary
will all combine to produce scattered SHRA/TSRA this afternoon,
through the early evening. The main problem is timing and how
widespread the activity becomes this afternoon. Two areas that
satellite/regional radar have been depicted that will have the
best chance of widespread SHRA/TSRA for the first couple of hours
will be near KRWF/KMKT and KAXN. Elsewhere, the main dilemma would
be outflow from the TSRA currently developing and where another
updraft develops. Although it is not the best scenario, VCTS
looks reasonable for the first several hours, then taking out VCTS
after 1-2z. This forecast has low confidence, but enough to
continue the VCTS or some TEMPOs based on the current radar
trends. The next concern is whether redevelopment occurs toward
12z from KRWF- KMSP-KRNH. This scenario has low confidence once
again, but based a mid-level trough holding back until Wednesday
afternoon, I wouldn`t be surprised to see more activity toward
sunrise.
KMSP...Timing and how long will the TSRA/SHRA continue this
afternoon is the main forecast concern. Confidence is high that
TSRA will develop in the vicinity, but timing remains low. Will
continue the same trend with most of the TSRA developing after
21z, and ending toward sunset. As previously mentioned, more
TSRA/SHRA is possible toward 12z. Winds will be generally from the
west- northwest, then north-northeast Wednesday.
/OUTLOOK FOR KMSP/
Wed evening...VFR. Wind NE 5 kts.
Thu...VFR. Wind NNE 5 kts.
Fri...VFR. Wind NE 5 kts.
Sat...VFR. Wind light/Variable bcmg SE 5 kts.
&&
.MPX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
&&
$$
SHORT TERM...JLT
LONG TERM...JPC
AVIATION...JLT